Mercury vapor lamp, metal halide lamp or high pressure sodium??

All buzz the same. The humming noise comes mainly from the ballast that limits the current to the lamps, because its core vibrates 50 times per sec.
The ballasts that are used in the US, tends to hum louder, either because the core is exposed (Unlike the European ballast), or it consists of an additional transformer winding to rise the 120V of the US to 240V.

The latter is imagined out of the finger. There are many factors why either ballast design could be louder than the other, and it will be down to the individual luminaire anyway

Carbon arc lamps buzz more.

Mercury vapor lamp, metal halide lamp or high pressure sodium??

All lamps have similiar buzzing sound.Mostly it depends on ballast how loud it would buzz.

dor123 -  In our case (50hz) the sound you get is from the vibration form the core which is actually at 100hz because it works on both sides of the sine wave. If you listen to a 50hz tone and 100hz you'll quickly find 100hz is closer but isn't as there is harmonics and the resonant frequencies of the core itself.

Mercury vapor lamps, Metal Halide and High Pressure Sodium bulbs are part of the HID family of bulbs. Light emitted from metal halide is white and from High Pressure Sodium bulb is amber orange. While mercury lamps produce white light with a bluish-green tint due to mercury's combination of spectral lines. Mercury vapor lamps is the least efficent member of the HID family due to lower light output.

Mercury vapor lamp, metal halide lamp or high pressure sodium??